Variable voltage motor control



Se t. 9, 1941. e. E. KING VARIABLE VOLTAGE MOTOR CONTROL Filed Nov. 29,1939 2 Sheets-Sheet l iNVENTOR Geo/"ye 5/0";

BY MK.

WITNESSES: yz/M ATTORNEY Sept. 9, 1941. KlNG 2,255,064-

VARIABLE VOLTAGE MOTOR CONTROL Filed Nov. 29, 1959 2 Sheets-Sheet 2WITNESSES: iNVENTOR WM GewyeE/Ohy: BY

Wm. M

ATTORNEY Patented Sept. 9, 1941 VARIABLE VOLTAGE Moron CONTROL George E.King, Wllkinsbur'g, Pa,

asslgnor to Westinghouse Electric & Manufacturing Company, EastPittsburgh, Pa...

Pennsylvania a corporation oi Application November 29, 1939, Serial No.306,667

20 Claims.

My invention relates to electric motor control systems, and moreparticularly to control systems for automatically controlling theoperation of motors used to drive reciprocating mechanisms, such'asplanets, draw-cut shapersyroll grinders, transfer tables, etc, by avariable voltage control.

My invention embodies improvements over the subject matter disclosed andclaimed in my applicatlon filed jointly with William R. Harding andWilliam F. Eames on March 30, 1938, Serial No. 198,884, and entitledVariable voltage control systems, and also improvements over '.,myprior.

application filed March 30, 1938, Serial No. 198,883, and entitledControl systems, and my prior application filled June 16, R938, SerialNo. 214,032, and entitled Variable voltage, motor controls.

In a conventional variable-voltage control, the motor is ordinarilyprovided with a separately excited field winding and the desireddirection of rotation of the motor is efiected by reversing the polarityof the energy supplied to the motor armature. The motor is arranged tobe energized from a generator which may be provided with a series fieldwinding to compensate for the IE drop in: the generator armaturecircuit; the armature circuit of the motor; the series field windingitself; and the leads interconnecting the generator and motorarmatures'. The generator is provided with a separately excited mainfield i winding, the current through which is. arranged to be controlledand reversed in order to operate the motor and the load attachedthereto, for

example, a planer platen, at various speeds in either direction oftravel. The excitation of the main field winding of the generator may becontrolled by means of a rheostat or the combination of variousresistors and suitable control devices for inserting various steps ofresistance in circuit with the main field winding. I

For eachposition oi the controller controlling the field current in thegenerator, there is a particular speed of operation of the motor, andthus the load, as a planer platen, that is, desired. Any departure inspeed from the desired value introduces undesirable operations of theload. If it were possible to maintain all of the conditions afiectingsuch a control constant the desired operation could be secured with thesimple conventional variable-voltage control just briefly explained. I

Since it is manifestly possible to maintain all the conditions aflectinga variable-voltage the load carried by, the motor. Differential field,

control constant, I use, with such a control, a regulator-generatorhaving a series field winding arranged to be responsive. to the currentsupplied to the motor, and a main, or shunt field winding arranged to beresponsive to the voltage applied to the motor. These field windings aredifferentially related to each other and are so disposed with referenceto each other that the regulator-generator, in operation, generates avoltage which is a function of the speed of, and

windings are also provided on the regulatorgenerator and are connected,respectively, in series circuit relation with the main field windings ofthe generator of the control system for opposing the combined action ofthe series and shunt field windings. The armature of theregulator-generator is arranged to be connected in series circuitrelation with these regulator-generator diflerential field windings andthe field windings of the generator of the control system and to thecontroller, which may be operated to independently vary the flow ofcurrent through the main generator field windings.

By a proper selection of the electrical characteristics and constants ofthe electrical units included with my system of control, and by aselection of a particular interconnection'of the electrical units and bymaking some minor compremises the proper functioning can be secured,that is, themotor speed can be made to be proportional to the setting ofcontroller regardless of: changes in ambient temperature; variations inthe load on the motor; direction of operation of the motor; rapidity ofthe voltage reversal on the motor terminals; and regardless of the manyother factors that would ordinarily prevent the desired operation of themotor.

Further, I have discovered that by a proper selection of the constantsof the electrical units ofa Wheatstone bridge, including the main fieldwindings of the main generator, the diflerentlal field windings of theregulator-generator, the armature of the regulator-generator andresistors, that the control eflect of the regulator can be made muchfaster and can be made substantially independent of the shape and slopeof the curve? indicating its saturation characteristics. Still otheradvantages may be obtained, which advantages will become more apparentfrom a study of the objects of my invention hereinafter stated and fromthe claims hereto appended.

"A broad object of my invention is to provide a system of control forvarying the voltage impressed on the terminals of a direct current motorin such manner that the speed selected for the motor by the control isattained in a relatively short time interval and is substan-- tiallyindependent of: the load on the motor;

the direction of rotation of the motor; and any selected butsubstantially independent of any variations in load and variations inspeed from the selected speed that tend to occur.

It is also an object to improve commutation, both for long stroke andshort stroke operation of a reciprocating member, of a generator and themotor connected to it and operating a reciprocating member.

One object of my invention is to shorten the useless portion of thestroke of a reciprocating device through a scheme of control affectin ormodifying the variable voltage control such as I disclose and claim inthe last patent application of mine above recited.

Another object of my invention is to make the speed regulation in avariable voltage sys-' tem substantially independent of the length ofthe stroke of a reciprocating member operated by a motor subject tovariable voltage control.

It is also an object of my invention to elimihate the defects, pointedout more in detail hereinafter, of the prior devices.

Other objects and advantages will become more apparent from a study ofthe following specificationand the drawings accompanying thespecification, in which:

Figure 1 is a side view. somewhat di mmatic, of a planer having a toolsupport and.

a motor for operating a planer platen; Fig. 2 is a plan-view of thesubject matter shown in Fig. 1;

Figs. 3 and 4 are diagrams which together show that portion of my systemof control embodyin some of the novel features of my invention; and

Fig. 5 is a diagrammatic showing of a variable voltage control includingthe novel features of my invention.

The circuit arrangements shown in the applications above noted showschemes of control using a bridge type speed regulator-generator as usedon planers and drives.

The regiflator-generator provides very close speed regulation over awide speed range. -The regulator-generator does not force theacceleration or retardation of the main motor. The rate of accelerationand retardation of the main motor is dependent on the time constant ofthe variable voltage generator shunt fields. This has been determinedrlmentally and is evident from an analysis of the circuit. As thecurrent changes in the variable voltage generator shunt fields and thevariable voltage generator terminal voltage changes accordingly, theregulatorgenerator field circuits remain nearly balanced.

The regulator-generator armature voltage therefore remains approximatelyzero. The only time the regulator generator armature generates a voltageis when there is an unbalanced cond tion existing in its field circuits.

similar machine tool Referring to the drawings, it will be noted thatthe regulator-generator armature circuit between junctions B and D (seeFig. 4) in conjunction with the bridge resistors R1 and R4 acts as adischarge resistor around the variable voltage generator shunt fields 5and d and consequently slows down the rate of change of the current bothin the building up and dying down.

Thisaction occurs at the end and the beginning of the cycle of operationwhen the regulator generator armature voltage is approximately zero. Allof the retardation and the initial part of the acceleration occurs atthe end of the stroke after the reversing limit switches are operated.This is usually considered as the useless part of the stroke as thelimit switches are operated at the point where the cutting tool leavesthe work. I

When operating on short strokes the motor is alternately acceleratingand retarding and never reaches a constant speed. The regulatorgenerator cannot do any good under these conditions and, in fact, causesslowing down of the operation. To improve the short stroke operation aresistor 9 was added in series regulator-generator armature to increasethe effective discharge resistance around the variable voltage generatorshunt fields. The ohmic value of the resistor 9 determines the number ofshort strokes that can be made ine given time. A

resistor is chosen to limit the maximum number short, circuit theresistor 9 for long stroke opera- I tion where good speed regulation isrequired.

While this scheme worked satisfactorily, it

I required attention on the part of the operator and had certaindisadvantages. If the manual switch was left open on long strokes poorcommutation as well as. poor regulation resulted. Poor commutationresulted because the motor accelerated to a higher speed, and thevariable voltage generator terminal voltage was higher on long strokesthan on short strokes. If the planer was operating on short strokes in apocket and the short stroke switch was closed inadvertently the strokewould lengthen and damage tool or work. Since the manual switch must beclosed on long strokes to secure good regulation and commutation thebenefits of fast stopping and acceleration were lost. This meant thetable drifted farther at the end of the stroke after striking the limitswitch and a larger percentage of the stroke was useless requiring moretime to complete a given operation. The term short stroke is ratherindefinite. and hard to define. The gear ratios on planers vary from,

four motor revolutions for one foot of table travel to fifteen motorrevolutions for one foot of table travel. This made it difilcult toissue any general instructions as to the maximum length stroke it wassafe to use with the short stroke resistor in the circuit. The limitcould be expressed only in motor revolutions since bad commutationresulted if a definite motor speed and terminal voltage were exceeded.

To avoid the above disadvantages I have developed. the scheme of controldisclosed and claimed in this application and in which I use a relay inplace of the manual switch for shorting the resistor 8 in series withthe regulatorgenerator armature. The operation of the relay with the.

the I is full automatic and requires no attention on the part of theoperator. The use of the relay eliminates all the disadvantages of themanual switch for short stroke operation and improves the long strokeoperation.

A still better understanding of the novel features of my invention maybe had from a study of a detailed discussion of the circuit arrangementand the novel function of my system of control. I

In the practice of my invention, I provide a variable-voltage control inwhich the motor M is mechanically coupled to drive a machine tool as aplaner platen I. The motor M is provided with a separately excited fieldwinding 2 which is arranged to be energized in a single direction onlythrough rheostat l2. A generator G is provided having its armature 3substantially directly electrically connected to the armature 4 of themotor. The control of the speed and acceleration of the motor and inconsequence the speed and acceleration of the planer platen armature ofthe motor.

and the direction of movement oi. the planer platen is effectedbyvarying the amount and direction of excitation of the field windings 5and 6 of-the main generator. effected in a few or in many stepsdepending upon the type of operation that is desired.

In order to maintain the speed of the motor M at various constant speedvalues corresponding'to a specific adjustment of the controller I usedfor controlling the current flowing through the main field windings ofthe generator, I use a regulator-generator R. This regulator-generator Ris arranged to measure the speed and load of the motor and the currentfiowing through the main field windings 5 and 5 of the generator. Thearmature 8 of the -regulator generator is arranged so that it may beconnected in series circuit relation with a permanent resistor 48' andwith the generator field windings 5 and 6, whereby the voltage generatedin the armature in response to the speed and load of the motor and thecurrent flowing through the generator field windings 5 and B will causea current to fiow through the main generator field windings 5 and 6,which current will be a function of the departure of the'motor speedfrom a predetermined value, corresponding to the particular setting ofthe controller 1 for the main field windings; that is, will correspondto the particular setting of the adjustable lead H) of the rheostat ll.

Under certain load and operating conditions, no voltage will begenerated in the armature of the regulator-generator R, since underthese conditions the speed of the motor M corresponds to the setting ofthe controller I, that is, corresponds to the adjustment of rheostats IIand I2. For all other conditions, however, a voltage will be generatedin the armature of the regulator-generator in such a direction andofsuch a value as to cause a current to flow through the main fieldwindings 5 and B of the generator G to still operate the motor at thedesired, or selected, speed.

In order to measure the speed of the motor M and load carried by themotor M, the regulator-generator R is provided with a series fieldwinding I through which all or a portion the current flowing from thegenerator G to the motor M flows, The regulator-generator is alsoprovided with a main field winding l which is connected to be responsiveto the voltage applied to the motor. These two field windings, namely,

This control may be I 4 and i5, are differentially related to each otherso that the resulting flux is a function of the speed of the motor M asmeasured by the counter-electromotive force of the motor. That is, themagnetomotive force produced by the series field winding 14 isproportional to the IR. drop of the motor armature 4, and themagnetomotive force produced by the main field winding ii of theregulator-generator is proportional to the voltage impressed across theterminals of the Thus, the resulting flux due to the differentialrelationship between the two field windings is a function of thecounterelectromotive force of the motor. Since this flux results fromthe combined action of the current fiowing through the motor armatureand the voltage applied thereto, it is also a function of the loadcarried by the motor. The voltage which is generated in the armature ofthe regulator-generator due to this resulting flux is then a function ofthe s eed of the motor and the load carried thereby.

It is desirable that any change in the voltage of the generator causedby the voltage generated in the regulator-generator armature andeffecting the current flow through the main field windings 5 and 6 ofthe generator G be immediately reflected in the voltage generated in thearmature 8 of the regulator-generator R. Such action is desired in orderto prevent hunting of the system. As soon as a voltage appears in thearmature of the regulator-generator indicating that the speed of themotor M has departed from the desired speed, a change in the fiow ofcurrent through the main field windings 5 and 6 of the generator G takesplace in such a direction as to tend to restore the speed of the motorto the desired speed. If some means is not provided for immediatelyeffecting a corresponding change in the corrective voltage generated inthe armature 8 of the regulator-generator R, the resulting change in theeffects of the series and main field windings l4 and I5 of theregulator-generator in response to the corrective effeet will take placetoo late. As a result, the speed of the motor will be altered more thanis desired and hunting will result.

In order to make the correction applied by the regulator-generatorproportional to the departure of the speed of the motor from the desiredspeed corresponding to a particular setting of the controller for themain field windings 5 and 6 of the generator G, a pair of differentialfield windings l6 and I1 are provided in the regulator-generator. Thesefield windings l6 and I! are connected in series with the main generatorfield windings 5 and 6, respectively. Thus any change in current whichflows through the main generator field windings 5 and 6 is immediatelyreflected in the voltage which is generated by the armature of theregulator-generator. It is then unnecessary to await the correction inthe speed of the motor, as reflected in the change in the efiectsproduced by the series and main field windings of theregulator-generator to correspondingly ailect the voltage generated bythe armature of the regulator-generator. The difierential field windingsl6 and I! of the regulator-generator are arranged to produce an effectin the same direction as the effect produced by the series field windingM of the regulator-generator and, therefore, they oppose or aredifierentially related to the eifect of the main field winding l5 of theregulator-generator.

There is always, then, a certain relationship between the speed and loadof the motor and the corrective effectcaused thereby in altering theflow of current through the main field windings of the generator. As aresult, the system is free from hunting and the speed of the motor ismain-' tained at predetermined values corresponding to various settingsof the lead III of the controller I regardless of the many variableconditions which would otherwise aflectthe speed, and cause it to changefrom the values desired.

As has been stated hereinbefore, it is desirable to eilect a correctiveaction in the current flowing through the main field windings and 6 ofthe generator G by means or the regulator-generator R, without alteringthe currents flowing through the main field windings 5 and 8 from theconthe motor.

I have discovered that a Wheatstone bridge arrangement may be combinedwith the controlfor machine tools to efiect the desired independentcontrol of the current flowing through the main field windings of thegenerator. I provide a Wheatstone bridge circuit in which thedifferential field windings l6 and I! of the regulatorgenerator and themain generator field windings 5 and 6 are respectively connected inseries circuit relation,'and form all of two or the branches of theWheatstone bridge circuit. The armature oi the regulator-generator isconnected across one pair or opposite terminals, as B and D, of theWheatstone bridge circuit while the remaining pair of terminals, as Aand C, is connected through some switches and through the controller lto an independent source 0! electrical energy. With such an arrangement,it is possible to vary the current flowing through the branches of thebridge containing the main field windings 5 and 5 of the generator G bymeans of the controller 1 independently of the current flow therethroughfrom the armature of the regulator-generator, and vice versa.

Referring more particularly to the drawings, the reference character Mdesignates generally the motor mechanically coupled to drive the planerplaten i of the planer it. A workpiece i9 is shown mounted on theplaten, and as the platen reciprocates, by reason of the reversingoperation of the motor M, the tool 2d mounted on the cross rail operateson the workpiece l9.

The motor M is substantially directly electrically connected to thegenerator G. The generator G has main field windings 5 and 8 and adifl'erential stabilizing field winding 2 i. The armature 3 of thegenerator G is mechanically coupled to the shaft 22 of the inductionmotor, or other prime mover P. This induction motor P is disposed to beconnected to the buses '23, 24 and 25 leading to a suitable source ofalternating current energy.

In order to properly control the motor M, I use a regulator-generatorgenerally designated R, which regulator-generator has the mechanicallycoupled to an induction motor 26. The motor 26 is-a relatively smallmachine, but has winding arrangements similar to the windingarrangements of motor P, so that the speed of the regulator-generator Rand the speed of the generator G, are, when in normal operation, the

same. It desirable, the regulator-generator may be mechanically coupledto armature 8 actual practice, since the dynamo-electric machines 28 andR are or about the same capacity, they will be built as a. unit havingthe same frame and shaft.

As shown in the drawings, the regulator-generator R is provided with aload main or shunt field winding I! (the prefix load indicating that itis connected in the load circuit), a pair of difierentlal field windingsl6 and I1 and a load series field winding l4. rows adjacent thesementioned field windings, difierential field windings I. and I! and theseries field winding II are so wound on the pole pieces of theregulator-generator R that they produce magnetomotive forces inthe samedirection, but

opposite to the direction of the magnetomotive force produced by themain or shunt field winding ll.

Assuming the generator G is' in operation through suitable operation ofa controller or motor starter 21, the starting of the motor Misdirection when the directional contactor 3| is operated. g

It is desirable to independently control the flow or current through themain field windings 5 and 6 of the generator G from two sources, one

or the sources comprising the exciter E across the armature terminalsof'which the rheostat II and the Wheatstone bridge are connected, andthe other'source comprising the armature 8 of the regulator-generator.For this purpose, I provide, as already suggested, a Wheatstone bridgecircuit comprising the customary four legs or branches, two of whichinclude the resistors R1 and R4 and the other two branches comprise, oneof them, the differential field wind-- 11-; it of theregulator-generator R and field winding e of the main generator G, andthe other or them, the field winding 8 of the main generator G, resistorR2: and difierential field winding ill of the regulator-generator R earmature 8 or the regulator-generator may have its terminals connectedto two of the opposite terminals or the Wheatstone bridge either throughresistors 9 and 34 or resistor 34 and switch 83; The other two oppositeerminals of the Wheatstone bridge may be connected to the exciter Ethrough circuits to be traced hereinafter. The series field winding H orthe regulator-generator R is connected, as illustrated, in series withan adjustable resistor Re disposed in the circuit connecting thearmatures 3 and 4 of the generator G and motor M, respectively. Anadjustable shunt 85 may be provided for adjusting the flow of currentthrough the series field winding N. The shunt field winding is isconnected through an adjustable resistor Re across the armatureterminals of the motor lid. The resistor R: is used to reduce the heatloss in the shunt field winding 85 and in consequence reduces to aminimum any change in resistance or the field winding it by reason ortemperature the shaft 22. In

changes.

oduction is an important item on machine I As indicated by the ar- Withthe devices of the prior art and also the systems oi control disclosedand claimed in the applications, hereinbefore mentioned, it was notpossible to design the field windings of the motor and generator, in avariable voltage control, for a small inductive time constant to thussecure the most rapid reversal.

In the drawings, I illustrate my contribution to the art in its simplestform. I show a resistor 9 in series with the armature of theregulatorgenerator and show no resistors at alldirectly in series withthe field windings and I6 and 6 and IT. with thi arrangement, thegenerator fields can be designed for a lower resistance and a highercurrent making them much faster. The legs of the bridge no longer needto be 50 ohms or some other high value but can be very much lower, thatis, any lower value and thus will draw more current fromthe main exciterE.

. The resistor 9 can be designed to make the regulator-generatorself-exciting as the regulator current must pass through this resistor.The arrangement permits not only a much better generator designprimarily oi the main generator but also of the regulator-generator.

So far as Fig. 4 is concerned, the showing is exactly the same as Fig. 4of the last hereinbefore recited application, however, the switch 33 isoperated in a radically difierent manner and by radically difierentmeans. Relay 200 and the elements that effect and afiect its operationare the important contributions made in this case.

The relay contact members 33in a small measure correspond to the manualswitch formerly used. Relay '0 operates these contact members 33. Thisrelay 200 has two coils, main or pickup coil 20! used to pick up therelay and which coil is connected in series with the reversing tswitches 2 02 and 203, inside the contacts of reversing contactors 30and 3|, and a hold-in coil 20 connected across the variable voltagegenerator terminals in series with a slow-down limit switch. The coil204 does not have sufiicient ampere turns to pick-up the relay armatureto close the contact members 33, but the coil is chosen of suchcharacteristics as to hold contact members 33 closed, after they havebeen closed by coil 20!, until the voltage of the variable voltagegenerator G decreases to a value where the commutation will besatisfactory after the resistor 9 is inserted. The variable voltagegenerator terminal voltage at which it is safe to insert the resistor 9varies with the ohmic value of the resistor 9 and also with thedifferent sizes of variable voltage generators.

By the use of my arrangement shown in Fig. 4, the resistors R1 and R4are designed to have a resistance value equal to the sum of theresistance values of the main generator and regulator fields in therespective opposite legs of the bridge and then it is necessary at thefactory to select the proper resistance value for only one resistor,namely, resistor 9, to make the regulator self-exciting.

The regulator-generator sends current through the maingenerator fieldsin the same direction as the excitation current when the generator isoperating near saturation. This is to correct for saturation of the maingenerator. The resistors R: and R2: in Fig. 3 .must,.thereiore, be ofsufllcient capacity to carry both the excitation and regulator current.The resistors R1 and R4 are subjected to the difference between theexcitation and regulator voltages and can be of less capacity.

with my new scheme, the two resistors R: and R2: are not needed andresistors R1 and R4 can be of much lower capacity. vides a circuitarrangement which permits the design of faster main generator fields, inwhich the adjustment is easier, in which iewer resistors are needed, andin which the resistors used can be of lower capacity.

If the attendant wishes to start the equipment he actuates the motorstarter 21 to thus cause the operation of prime mover P and theinduction motor 26. Regulator-generator R, the exciter E back contactmembers 12 and the main generator G are thus caused to operate.Operation of the motor starter also establishes an energizing circuitfor the coil 38 of the contactor 39, whereupon the contact members llare closed to set up circuit connections to be described later.

When the motors P and 26 are up to full speed, the voltage of exciter Ewill be of full value and in consequence the main motor M may bestarted. Since the exciter voltage is up to normal, a predetermineddirect-current potential is placed across buses 4| and 52.

Energization of buses 4| and 42 provides an energizing circuit for thecoil 43 of the relay 44 controlling the field 2| for generator G in awell known manner.

The field winding 2 of motor M is also energized from buses ll and 42.The field circuit may be traced from bus ll through conductor 48, thefield rheostat comprising the resistor I2 and adjustable lead HI,conductor 49, field winding 2 to bus 42. An additional but lowresistance circuit is also established for the field winding 2, whichadditional circuitmay be traced from energized conductor 43through'contact members 84 of starting control relay 85, shunting thefield rheostat.

To effect normal operation of motor M, either one of the switches 28 and29 should be operated. Let switch 28 be the forward control push-buttonswitch. To effect forward operation, that is, an operation in the cutdirection, the attendant depresses the switch 28. A circuit isimmediately established from bus 4| through stop switch 59, contactmembers 40, coil of control relay 5|, conductor 52, reverse limit switch53 of the cut limit switch 013, return starting push-button switch 29,the lower terminals of switch 28, conductoril, actuating coil 55 ofregulator-generator control relay 56 to the bus 42.

Operation of relay 5| opens the contact members 60 and GI to deenergizecoil 3 to thus in a short interval of time open the circuit for thestabilizing field 2|.

Operation of relay 56 establishes its own holding circuit throughcontact members 59 and resistor l0, and also closes members 32,13 andTi.

Closure of contact members 1i establishes a circuit from energizedconductor 52 through limit switch 53, switch 29, contact members Tl,actuating coil 13 of directional contactor 3i, and

of directional contacswitches or contact tor 30 to bus 42.

Another circuit may be traced from the closed contact members 69 throughcoil 18 of the start- My scheme thus pro-.

will naturally be that field 2 is heavily excited and a large startingtorque is produced by motor l.

Since coil '33 is energized, contact members 89, BI and 82 are closed. Agenerator field control circuit is thus established-from bus ll throughconductor 19, contact members 80, to junction C. From junction C onecircuit may be traced through generator field winding 6, regulator fieldwinding ll, junction D, resistor R1, to junction A and another circuitmay be traced from junction C through resistor R4, junction B, regulatorfield l6, generator field winding 5 to junction A. The armature circuit,including armature 8, adjustable resistors 9 and 34 and shunting contactmembers 33, is connected across junctions B and D. From junction A, thegenerator field control circuit is through a permanent resistor 48,resistor R1, controller 1, conductors 88, 89 and 99, contact members 8!to bus 42.

Closure of contact members 32 shunts resistor R7 so that the fieldvoltage of exciter E is applied as modified by controller I and resistor48'. The planer will thus run in the out direction and since thecounter-electromotive force of motor M builds up rapidly, coil 92 ofrelay 85 will be energized. Coils l8 and 92, thus acting together, openthe contact members 84 and the motor M thus has its excitation decreasedand thus operates at the cutting speed determined by the controllersetting for the generator G. Since the generator voltage is at fullvalue, coil 204 is fully energized and since coil 29! is fullyenergized, contact members 33 are closed and resistor 9 is. shunted.

Assuming the planer isrunning at full cutting speed and the circuits inthe arrangement discussed. Near the end of the cut stroke the out limitswitch CLS is operated. Contacts 53 deenergize coil 13 of the cutdirectional contactor and contacts 53' deenergize coil 2M of relay 290.The contact members 33 may or may not open at the instant coil 20! isdeenergized. Assuming it is safe to insert resistor 9 in series with thearmature 8 when the terminal voltage of the variable voltage generator Gis 200 volts, then the coil 294 will-keep the contact members 33 closedfor all terminal voltages above 200 volts. When the terminal voltagedecreases to 200 volts, the contact members 33 open to insert theresistor 9 in series with the armature 8. The variable voltage generatorterminal voltage decreases rapidly to zero and builds up in thereverse'direction since contact member 30 will be energized from bus 4| throughstop switch 59, contact members 40, coil 50, return limit switch RLS,out push-button switch 28, contact members l3, coil I03, back contactmembers 83 to bus 42.

The main motor reverses and the table starts in the return direction.The same dog 93 which tact members 33 open to again insert resistor 9 inthe circuit of armature 8.

The operation as described shows that the resistor 9 is inserted inseries with the regulator-generator armature only at the end of thestroke after the limit switch has been operated and then only after theterminal voltage of generator G has decreased to a value that willinsure good commutation. j The value of voltage used, that is, 200volts, is for purposes of illustration only.

Tests using my novel scheme of control revealed that the number of shortstrokes could be increased from 28 to per minute and revealed somesaving on the long strokes. The most improvement is on short strokesbecause the motor is constantly reversing. The greatest advantage onlong strokes is the decrease in the overtravel beyond the limit switchesthus permitting higher operating speeds when working in blind pockets oragainst shoulders.

The'relay 200 connection may, of course, be

'in various ways to obtain the same or similar results. I do not wish tobe limited to the particular circuit arrangement shown but wish to belimited only by the scope of the claims hereto appended.

I claim as my invention:

1. In a system of control for controlling the excitation of a generator,in combination, a main generator having an armature winding and having apair of field windings connected in two opposite legs of a'balancedWheatstone bridge, a load connected in series with thegenerator-armature, a regulator-generator and adjustable resistorconnected in series with the armature of the regulator-generatorconnected across two of the junctions of the Wheatstone bridge, a shuntcircuit for the adjustable resistor, switching means responsive to thevoltage of the main generator adapted to control the connection of theshunt circuit, said regulator generator havoperated the cut-limit-switchCLS resets this switch to closed position completing the circuit forcoil 21", causing the contacts 33 to close and thus short-circuit theresistor 9.

Near the end of the return. stroke, the return-limit-switch, RLS, isoperated and one con- "tact, as I92, deenergizes coil I03 of contactor39 and the other, as I02, deenergizes coil 29!. Contact members 33 are,however, again held closed by coil 2M until'the voltage of the generatorG has decreased below a given value, as 200 volts. After the voltage hasdecreased; coning a pair of field windings 'energizable respectively bythe voltage of the main generator and by the load'current andhaving apair of field windings one connected in one leg of the bridge in serieswith one of the main generator field windings and the other connected inthe opposite leg of the bridge in series with the other maingeneratorfield winding and a pair of bridge balancing resistors connected in theother two opposite legs of the bridge, and a source of variable directcurrent voltage connected across the other two junctions of the bridge.

2. In a system of control for controlling the excitation of a generator,in combination, a main generator having an armature winding and having apair of low impedance field windings connected in two opposite legs ofthe balanced Wheatsone bridge, a load circuit connected in series withsaid armature winding, a regulatorgenerator and adjustable resistorconnected in series with the armature of the regulator generatorconnected across two of the junctions of the Wheatsone bridge, a shuntcircuit for the adjustable resistor, switching means responsive to thevoltage of the main generator adapted to control the connection of theshunt circuit, said opposite leg 01 the bridge in series with the other,of the low impedance main generator field windings, and a pair of bridgebalancing resistors connected in the other two opposite legs of thebridge.

3. In a system of control for a motor, in combination, a generatorhaving a pair of low impedance field windings, a motor, substantially oithe capacity of the generator, directly connected to the generator andhaving a field winding, an exciter, a controller adapted to alter theexcitation or the motor field winding depending on the direction ofrotation of the motor and adapted to reverse the connection of the twogenerator field windings to the exciter, a regulator-generator having anarmature winding, and four field windings, an adjustable resistor inseries with the armature winding, a shunt circuit for the adjustableresistor, switching means responsive to the voltage or the maingenerator adapted to control the connection of the shunt circuit, abalanced Wheatstone bridge circuit having two or its junctions connectedthrough the controller to the exciter and having the armature of theregulator-generator and the resistor in series 4. In a system of controlfor controlling the voltage of a generator, the sub-combination o! amain generator, a Wheatstone bridge including a regulator-generatorconnected across two of the Junctions oi the bridge, a source ofenergizing potential connected across the other two Junctions, meansresponsive to the voltage or the generator for varying the resistancevalue or the generator circuit of the regulator generator, a

CJI

the armature current of the generator and motor.

7 windings for varying the resistance value of the armature circuit ofthe generator having the four field windings, a source of energizingpotential connected across the other two junctions, and the othergenerator being connected to a load and the remaining two field windingsof the generator having four field windings being connected to beresponsive, respectively, to the voltage and the load of the generatorhaving two field windings.

6. In asystem of control, in combination, a Wheatstone bridge, a pair ofadjustable resistors in each or two of the oppositely disposed branches,anda pair of generators, one of said generators having four fieldwindings and the other of said generators having at least two lowimpedance field windings, one of the field windings of the firstgenerator and one of the low impedance field windings constituting allor one branch of the'Wheatstone bridge, and a second field winding ofthe first generator and one or the low impedance field windings of thesecond generator constituting all of the remaining branch of theWheatstone bridge, said remaining two field windings oi the firstgenerator being connected so as to be energizable respectively inaccordance with the potential 01' the second generator and with thearmature current of the second generator, a source of potentialconnected across two junctions of the Wheatstone bridge. the armature ofthe generator having the four field windings connected across the othertwo junctions of the Wheatstone bridge, and means responsive to thevoltage of one generator adapted to vary the resistance value of thearmature circuit of the other generator.

7. In a variable voltage control system, in combination, a motor, acontrol source of energy, a

' generator electrically: connected to the motor,

low impedance main generator field winding and a field winding for theregulator-generator in one leg of the bridge, a second low impedancemain generator field winding and a field winding of theregulator-generator in the opposite leg of the Wheatstone bridge, and. apair 01' resistors in the two opposite legs oi. the bridge'and tworegulator-generator field windings connected respectively to beresponsive to the generator voltage and generator load current.

5. In a system or control, in combination, a Wheatstone bridge, a pairof adjustable resistors in each 01' two of the oppositely disposedbranchis, and a pair of generators. one 01' said generators having fourfield windings and the other of said generators having at least tworelatively low impedance field windings, one of the field windings ofthe first generator and one 01' the low impedance field windingsconstituting all oi. one branch of the Wheatstone bridge, and a secondfield winding of the first generator and one of the low impedance fieldwindings of the second generator constituting all or the remainingbranch of the Wheatstone-bridge, the one of said generators having fourfield windings being connected to two of the Junctions of saidWheatstone bridge and including means responsive to the voltage of thegenerator having the two field.

pedance field windings,

a pair of main low impedance field windings for said generator, acontroller for connecting the main low impedance field trol source ofenergy in a steps to eiiect changes in windings to said conplurality ofdiirerent the speed 0! the motor, and a regulator-generator connected tovary the fiow of current through the main low imindependently of thecurfrom said control source the speed of said motor at rent flowtherethrough of energy, to maintain predetermined or selected diirerentspeeds, each speed corresponding to the step selected by saidcontroller, said regulator-generator having an armature winding, a loadseries field winding, a load shunt field winding, a pair of diflerentialfield windings, said series and shunt field windings being disposed tobe difierentially related to each other and respectively responsive tothe current and voltage supplied to said motor from said generator, saidarmature windings oi said regulator-generator, including in its armaturecircuit a resistor adapted to be connected in series circuit with saidarmature winding, means responsive to the voltage of said generator forshunting said resistor, and means for also adjusting the resistancevalue of said resistor, being connected across one pair oi oppositeterminals of a normally balancedwheatstone bridge circuit, the remainingpair of terminals of said bridge circuit being connected through saidcontroller to said control source of energy, one of the arms of saidbridge circuit including only one oi the pair of said main low impedancefield windings, and in series circuit therewith, only one of the saidpair or difierential field windings or said regulatorgenerator and thediametrically opposite arm of said bridge circuit including only theother of the said pair of main low impedance field windings and, inseries circuit therewith, only the other of said pair of differentialfield windings of said regulator-generator.

8. In a; variable voltage control system, in combination, a motor, acontrol source of energy, a generator electrically connected to themotor, a pair of main low impedance field windings for said generator,acontroller for connecting the main low impedance field windings to saidcontrol source of energy in a plurality of different steps to effectchanges in the speed of the motor, and a regulator-generator connectedto vary the flow of current through the main low impedance field windingindependently of the current fiow therethrough irom said control sourceof ener y, to maintain the speed of said motor at predetergenerator forvarying the resistance value of said resistor being connected across onepair of opposite terminals of a normally balanced Wheatstonebridgecircuit, the remaining pair of terminals of said bridge circuit beingconnected through said controller to said control source of energy, oneof the arms of said bridge circuit including only one of the pair ofsaid main low impedance field windings and in series circuit therewith,one of the said pair of diflerential field 'windings of saidregulator-generator, and the mined or selected difierent speeds, eachspeed corresponding to the step selected by said controller, saidregulator-generator having an armature winding, a load series fieldwinding, a load shunt field winding, a pair of difierential fieldwindings, said series and shunt field windings being disposed to bedifierentially related to each other and respectively responsive to thecurrent and voltage supplied to said motor from said generator, saidarmature winding of said regulator-generator, including in its armaturecircuit a resistor adapted to be connected in series circuit with saidarmature winding, and means responsive to the voltage of said generatorfor also adjusting the resistance value of said resistor, beingconnected across one pair oi opposite terminals of a normally balancedWheatstone bridge circuit, the remaining pair of terminals of saidbridge circuit being connected through said controller to said controlsource of energy, one of the arms of said bridge circuit including onlyone of the pair of said main low impedance field windings and one of thesaid pair of differential field windings of said regulator-generatorconnected in series circuit therewith and the diametrically opposite armof said bridgecircuit includingthe other of the said pair of main fieldlow impedance windings and, in series circuit therewith, the other ofsaid pair of differential field windings of said regulator-generator. P

9. In a variable voltage control system, in combination, a motor, acontrol source of energy, a

generator electrically connected to the motor, a pair of main lowimpedance field windings for said generator, a controller for connectingthe main field windings to said control source of energy in a pluralityof diflerent steps to effect changes in the speed of the motor, and aregulator-generator connected to vary the fiow of current through themain low impedance field windings, independently of the current fiowtherethrough ,from said control source of energy, to maintain the speedof said motor at predetermined or selected difierent speeds, each speedcorresponding to the step selected by said controller, saidregulator-generator having an armature winding, a load series fieldwinding, a load shunt field winding, 2, pair of difierential fieldwindings, said series and shunt field windings being disposed to bedifferentially related to each other and respectively responsive to thecurrent and voltage supplied to said motor from said generator, saidarmature winding of said regulatorgenerator, including in its armaturecircuit a resis er adapted to be connected in series circuit with saidarmature winding, means in series with the armature and responsive tothe voltage oi said said control source of energy in a plurality of dif-1 ferent steps to effect changes in the speed of the motor, and aregulator-generator connected to vary the flow of current through themain low impedance field windings, independently of the current flowtherethrough from said control source of energy, to maintain the speedof said motor at predetermined,.or selected, different speeds, eachspeed corresponding to the step selected by said controller, saidregulator-generator having an armature circuit including an'armaturewinding, a load series field winding, a load shunt field winding, a pairof difierential field windings, said series and shunt field windingsbeing disposed to be difiere'ntially related to each other andrespectively responsive to the current and voltage supplied to saidmotor from said generator, means for varying the resistance of saidarmature circuit from a given minimumto a given maximum, said armaturewinding and series adjustable resistor being connected across one pairof opposite terminals of a normally balanced Wheatstone bridge circuitand including means responsive tothe voltage of said generator forautomatically varyingthe resistance value of said adjustable resistor,the remaining pair of terminals of said bridge circuit being connectedthrough said controller to said control source of energy,- one of thearms of said bridge circuit including only one of the pair of said mainlow impedance field windings in series circuit therewith, and one of thesaid pair of differential field windings of said regulator-generator andthe diametrically opposite arm of said bridge circuitineluding only theother of the said pair of main low impedance field windings and, inseries circuit therewith, the other of said pair of difl'erential fieldwindings of said regulator-generator.

11. In a system of control, in combination, a Wheatstone bridge, a pairof resistors in each of two of the branches, and a pair of generators,one

of said generators having four field windings and of said Wheatstonebridge, said remaining two i to the second 2,255,064 field windings orthe first generator being connected respectively across the armatureterminals of the second generator and in the armature circuit of thesecond generator to thus be responsive to the voltage and armaturecurrent respectively of the second generator, and said generator havingthe four field windings having its armature connected across two of thejunctions of the Wheatstone bridge, and means responsive to the voltageof the generator adapted to vary the resistance value of the armaturecircuit of the generator having the four field windings.

12. In a speed regulator for an adjustable speed reversing power drivenmechanism in which an armature 01 a generator driven at relativelyconstant speed is substantially directly connected to an armature of apower motor whose speed is adjusted by changing the voltage of the saidgenerator armature, in combination: a first relatively low impedancefield for said generator; a second relatively low impedance field forsaid generator, a regulator generator having a resistance adjustablearmature, means responsive to the voltage of the generator forautomatically varying the resistance value of the regulator-generatorarmature, said regulator-generator having a first, a second, a third anda fourth field; said first regulator field being connected so thatcurrent proportional to that fiowing between the generator and motorarmatures fiows in it; said second regulator field being connected sothat a current proportional to the voltage across the terminals of saidmotor flows in it; and a Wheatstone bridge circuit having fourJunctions, said circuit comprising an adjustable impedance deviceconnected between the first and second Junctions; the first lowimpedance field or said generator field of said regulator in seriescircuit relation connected directly to the second and third Junctions; asecond adjustable impedance device connected to the third and fourthJunctions and said second low impedance generator field and said fourthregulator field in series circuit relation connected to said fourth andsaid first Junctions; the armature of said regulator generator beingconnected to a circuit between the first and third junctions and aseparate voltage supply of adjustable value being connected and fourthjunctions.

13. In a system of control for a motor, in combination, a Wheatstonebridge, a pair or adjustable resistors in each of two of the branches, apair of generators, one of said generators having four field windingsand the other of said generators having at least two relatively lowimpedance field windings, one oi the field windings of the firstgenerator and one 01 the low impedance field windings of the secondgenerator, connected in series circuit relation, being alone connectedin one of the branches of the bridge and a second field winding thefirst generator and the remaining, or second, field low impedancewinding of the second generator, connected in series, being aloneconnected in the remaining branch of the said Wheatstone bridge, saidremaining two field windings of the first gen erator being connectedrespectively across the armature terminals or the second generator andin the armature circuit of the second generator to thus be responsive tothe voltage and armature current respectively oi the second generatorand a motor connected across the armature terminals of the secondgenerator, the generator having the four field windings being connectedto two of the Junctions of the Wheatstone bridge, and a source ofvoltage connected to the remaining junctions of the Wheatstone bridge,and means responsive to the voltage of one-0t said generators adapted tovary the resistance value or the armature circuit or the othergenerator.

14. In a system or control tor a motor, in combination, a Wheatstonebridge, a pair or adjustable resistors in each 0! two of the branches, a

pair of generators, one of said generators having four field windingsand the other of said generators having at least two relatively lowimpedance field windings, one of the field windings of the firstgenerator and one of the low impedance field windings oi the secondgenerator, connected in series circuit relation, being alone connectedin one of the branches of the bridge and a second field winding of thefirst generator and the remaining, or second, field low impedancewinding of the second generator, connected in series, being aloneconnected in the remaining branch oi. said Wheatstone bridge, saidremaining two field windings oi the generator having four field windingsbeing connected to be responsive, to the load and voltage, respectively,of the generator having the two field windings, and the armature of thegenerator having the tour field windings being connected to two 01 thejunctions of the Wheatstone bridge, a source or energizing potentialconnected across the other two junctions and means responsive to thevoltage of one of said generators adapted to vary the resistance value01 the armature circuit of the other generator.

15. In a system 01 control ior a motor, in combination, a Wheatstonebridge, a pair of adjustable resistors in each of two of the branches, apair of generators, one of said generators having four field windingsand the other oi said generators having at least two relatively lowimpedance field windings, one of the field windings of the firstgenerator and one of the low impedance-field windings o! the secondgenerator, connected in series circuit relation, being alone connectedin one of the branches of the bridge and a second field winding of thefirst generator and the remaining, or second, field low impedancewinding of the second generator, connected in series, being aloneconnected in the remaining branch of said Wheatstone bridge, saidremaining two field windings oi the first generator being connectedrespectively across the armature terminals of the second generator andin the armature circuit of the second generator to thus be responsive tothe voltage and armature current respectively of the second generatorand a motor connected across the armature terminals of the secondgenerator, said first generator being connected across two oi. thejunctions of the said Wheatstone bridge, a source or energizingpotential connected across the other two junctions and means responsiveto the voltage of one of said generators adapted to vary the resistancevalue of the armature circuit of the other generator.

16. In a system of control for a motor, in combination, a Wheatstonebridge, a pair of adjustable resistors in each of two or the branches, apair of generators, one of said generators having i'our field windingsand the other or said generators having at least two relatively lowimpedance field windings, one of the field windings or the firstgenerator and one or the low impedance field windings oi the secondgenerator, connected in series circuit relation, being alone connectedin one of the branches oi the bridge and a second field winding of thefirst generator and the remaining, or second, field low impedancewinding of the second generator, connected in series, being aloneconnected in the remaining branch of said Wheatstone bridge, said firstgenerator'being connected across two of the junctions of the saidWheatstone bridge, a source or energizing potential connected across theother two junctions and the remaining two field windirrgs oi thegenerator having four field windings being connected to be responsive tothe voltage and load, respectively, of the generator having thetwo fieldwindings, and means responsive to the voltage of one of said generatorsadapted to vary the resistance'value oi the armature circult of theother generator.

17. In a system of control, in combination, a.

Wheatstone bridge, a pair of resistors ineach of two of the branches,and a pair of generators, one of said generators having an, armature andan adjustable resistor'in series therewith and four field windings andthe other of said generators having at least two relatively lowimpedance field the second generator to thus be responsive to thevoltage and armature current respectively 05: the

second generator, a source of direct-current energy connected across twoof the junctions of said Wheatstone bridge, and a motor connecteddirectly to said second generator, said first generator armature andresistor in series therewith being connected to the remaining junctionsoisaid Wheatstone bridge, andmeans responsive to the voltage of one ofsaid generators adapted to vary the resistance value of the armaturecircuit of the other generator. T V Y l8. In a system of controLflincombination, a Wheatstone bridge, a pair of resistors in'each of two ofthe branches, and a of generators, one of said generators having anature and an adjustable resistor in series therewith and four fieldwindings and the other of d generators having at least two relativelylow impedance held windings, one oi the field windings of the c ancesfirst generator and one of the low impedance field windings of thesecond generator, connected in series circuit relation, being aloneconnected in one of the branches oi the bridge and a second fieldwinding of thhrst generator. and the remaining, or second, low impedancefield winding of the second generator, connected in series, being aloneconnected in the remaining branch of said Wheatstone bridge, saidremaining two field windingsof the first generator being connectedrespectively across the armature termia nals of the second generator andin the armature.

circuit of the second generator to thus be responsive to the voltage andarmature current respectively oi the second generator, a source ofdirect-current energy connected across two of the junctions of saidWheatstone bridge, and a motor connected directly to said secondgenerator, said first generator armature and resistor inseries therewithbeing connected to the remaining junctions of said Wheatstone bridge,means for varying the voltage of said. sourcein predetermined steps, andmeans responsive to the voltage of one of said generators adapted tovary the resistance value oi the armature circuit of the othergenerator.

19. An electrical control system comprising, in combination, a drivingmotor, a machine tool element driven thereby, means for ener saiddriving motor including a generator having a main control fieldiwinding,which generator has an armature in loop circuit relationship with thearmature of the driving motor, a regulating generator having a controlfield winding in circuit relationship with said loop circuit so that itscurrent is a function of a variable electrical quantity existing in saidloop circuit, and a compensating -field winding or said regulatinggenerator in loop circuit relationship with-the regulating 1 generatorarmature and said generator main control field wing.

' 20. An electrical control system comprising, in combination, a drivingmotor, a machine tool element driven thereby, means for energizing saiddriving motor including a generator having a no control field winding,which generator has an armature in'loop circuit relationship with thearmature of the driving motor, a regulating generatorhaving a controlfieldnvinding in circuit relationship with said loop circuit so that itscurrent is a function of a variable electrical quantity existing in saidloop circuit, and a primary current source serving as a pattern andhaving a difierential sheet on said regulating generator control ding soas to differentially control the excitation of said regulatinggenerator.

GEOE E. G.

